Polysulfone is a special engineering plastics of great importance, which has long been used as a strategic national defense industry material ever since its successful development. Bisphenol A polysulfone PSF is a type of polysulfone resin with the maximum yield, the main chain of molecules of which consists of isopropylene, ether bond, sulfuryl and phenylene. These groups endow this type of polymer with excellent high-temperature resistance and remarkable mechanical properties. Therefore, bisphenol A polysulfone PSF is widely applied in many fields such as aviation, aerospace, national defense, electronics, electrics, medical treatment, nuclear power, oil well, ships, magnetic wires, military industry, automobile manufacture and food processing, etc.
Polysulfone is usually synthesized in industry by the method of double-feeding, which requires two reaction vessels, i.e., a salt forming kettle and a reaction kettle. Bisphenol A firstly reacts with a sodium hydroxide solution in dimethyl sulfoxide as the solvent to generate bisphenol A sodium salt, at the end of the salt forming reaction, the water entrainer is distilled off, then the resultant solid 4,4′-dichlorodiphenyl sulfone is added under the protection of nitrogen gas and stirred, followed by gradually increasing the temperature for polycondensation under 150 to 160° C. to generate polysulfone, where the polymerization lasts for about 3 h (which is controlled by viscosity). The polymerization involves complicated steps, a complex process, a long reaction time, and a high energy consumption. The salt forming reaction lasts for a long time, and the temperature inside the reaction kettle reaches 160° C. at the end of salt formation. To ensure that the polycondensation in the next step is not too violent, it is necessary to firstly reduce the temperature to 120° C., then increase the temperature for polycondensation; moreover, water formed from the salt forming stage should be removed from the system so as to inhibit decrease in monomer concentration and the side reaction of hydrolysis of halogen-containing monomer under high temperatures, and thus enough time for water removal should be guaranteed, normally between 2.5 to 8.5 h, as a result, the whole period from the beginning of the salt forming reaction to the completion of polycondensation takes as long as 18 h. In addition, the feeding hole needs to be opened for double-feeding, thereby the residual toluene vapor after water removal escapes from the reaction kettle, which is likely to cause damages to operators and pollute the air. The polycondensation in the above industrial synthesis process belongs to solution polymerization. In the later stage of the solution polymerization, the system viscosity is high, thus the after-treatment is in need of the addition of a large amount of organic solvent to reduce the viscosity. However, use of organic solvent in a large amount not only wastes energy and contaminates the environment, but also increases industrial costs. In addition, due to restrictions on solubility and boiling point of the organic solvent, the solvent type is very limited, most of them being sulfones. This type of solvent is often toxic, quite harmful. Finally, the industrial product obtained by the industrial synthesis process hereinabove has a low molecular weight. A product manufactured by Shanghai Shuguang Chemical Plant, which prepared the early polysulfone domestically, has a molecular weight of 20,610 to 27,840.
Ionic liquid, which replaces the traditional organic solvent as the reaction medium, has prominent advantages. For example, it is non-volatile, with a negligible vapor pressure and an excellent thermostability, and is easy for recycling. Furthermore, the ionic liquid can be adapted to different polycondensation systems due to the designability of its substance structure and natures. As currently reported, the ionic liquid has been successfully applied to polymerizations like active polymerization, controllable free radical polymerization, anionic and cationic polymerization, polycondensation (limited to synthesis of polyester, polyamide, polyimide, etc). The application of ionic liquid in nucleophilic substitution polycondensation reaction for preparation of engineering plastics polysulfone has not been reported up to now.